The present invention relates to a magnetic recording medium which is employed in a magnetic disk apparatus and the like.
A widely employed magnetic recording medium is of an in-plane recording type in which most of the easy-magnetization axes in the magnetic film are oriented horizontally with respect to the substrate. However, in such an in-plane magnetic recording medium, per-bit volume becomes exceedingly small and read-write characteristics may deteriorate when recording density is increased.
In contrast, in a perpendicular magnetic recording medium, in which most of the easy-magnetization axes in the magnetic film are oriented vertically with respect to the substrate, recording density can be increased without deterioration of read-write characteristics. Therefore, a perpendicular magnetic recording medium has recently become of interest, and magnetic recording medium structures suitable for perpendicular magnetic recording have been proposed.
For example, Japanese Patent Application Laid-Open (Kokai) Nos. 58-77025 and 58-141435 disclose that Ti is employed as a material for producing an undercoat layer of a perpendicular magnetic film comprising a Co alloy material. In addition, Japanese Patent Application Laid-Open (Kokai) No. 8-180360 discloses that an alloy of Co and Ru is employed as a material for producing the undercoat layer.
In recent years, there has been demand for magnetic recording media of higher recording density, and in accordance with this trend, improvement of noise characteristics has been required. However, conventional magnetic recording media are not necessarily satisfactory in terms of noise characteristics, and thus there has been demand for a magnetic recording medium that exhibits excellent noise characteristics.
Meanwhile, in a conventional magnetic recording medium, particularly when recording density is increased, a thermal fluctuation phenomenon may arise. The term xe2x80x9cthermal fluctuation phenomenonxe2x80x9d refers to a phenomenon in which recording bits become unstable and recorded data are lost thermally. When such a phenomenon occurs, read-write output of recorded data may lessen with passage of time in a magnetic recording apparatus.
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium which exhibits excellent noise characteristics and rarely causes a thermal fluctuation phenomenon.
The present invention provides a magnetic recording medium comprising a substrate, a first perpendicular magnetic film, and a second perpendicular magnetic film in order, wherein the magnetic anisotropy energy of the first perpendicular magnetic film is higher than that of the second perpendicular magnetic film.
Preferably, the first perpendicular magnetic film has a magnetic anisotropy energy of 5xc3x97106 erg/cc or more.
Preferably, the ratio of residual magnetization to saturation magnetization in the first perpendicular magnetic film is 0.9 or more.
The first perpendicular magnetic film may be a multi-layer film in which layers of Co material, and Pt or Pd material are repeatedly stacked; an amorphous film containing a rare earth element; or an ordered alloy, e.g., L10-structured FePt, CoPt, (Fe(1xe2x88x92n)Con)50 Pt50 (n: 0-0.99).
Preferably, the first perpendicular magnetic film has a thickness of 1-175 xc3x85, more preferably 1-100 xc3x85.
Preferably, the second perpendicular magnetic film comprises any alloy of CoCrPt, CoCrTa, and CoCrPtX (X: one or more species selected from among Ta, Zr, Cu, Re, Nb, Si, Ge, and B).
In the magnetic recording medium of the present invention, a non-magnetic intermediate film of hcp structure may be provided under the second perpendicular magnetic film.